Effects of Low‐Carbon Energy Adoption on Airborne Particulate Matter Concentrations With Feedbacks to Future Climate Over California

Abstract

California plans to reduce emissions of long‐lived greenhouse gases (GHGs) through adoption of new energy systems that will also lower concentrations of short‐lived absorbing soot contained in airborne particulate matter (PM). Here we examine the direct and indirect effects of reduced PM concentrations under a low‐carbon energy (GHG‐Step) scenario on radiative forcing in California. Simulations were carried out using the source‐oriented WRF/Chem (SOWC) model with 12 km spatial resolution for the year 2054. The avoided aerosol emissions due to technology advances in the GHG‐Step scenario reduce ground level PM concentrations by ~8.85% over land compared to the Business‐as‐Usual (BAU) scenario, but changes to meteorological parameters are more modest. Top‐of‐atmospheric forcing predicted by the SOWC model increased by 0.15 W m−2, surface temperature warmed by 0.001 K, and planetary boundary layer height (PBLH) increased by 2.20 cm in the GHG‐Step scenario compared to the BAU scenario. PM climate feedbacks are small because the significant changes in ground level PM concentrations associated with the GHG‐Step scenario are limited to the first few hundred meters of the atmosphere, with little change for the majority of the vertical column above that level. As an order‐of‐magnitude comparison, the long‐term effects of global reductions in GHG emissions (RCP8.5–RCP4.5) lowered average surface temperature over the California study domain by approximately 0.76 K. The effects of long‐lived climate pollutants such as CO2 are much stronger than the effects of short‐lived climate pollutants such as PM soot over California in the year 2054.